This invention generally relates to the placement and reflow of solder balls on substrates used in the electronics field. More particularly, the present invention relates to an improved apparatus and method for the high speed placement and reflow of solder balls using a high energy laser and an inert gas to ensure repeatable, precise placement and reflow at rates exceeding 40 balls per second.
With the increased demand for high speed and miniaturized electronics, the need to reliably and repeatably produce integrated circuit (IC) substrates and substrates used for semiconductors has also grown. Such electronic components include plastic ball grid arrays (xe2x80x9cPBGAxe2x80x9d), chip scale packages (xe2x80x9cCSPxe2x80x9d), and direct chip attach (xe2x80x9cDCAxe2x80x9d) components. One important step in the manufacture of such substrates is the placement of solder connection points in specific locations on the substrate.
With the expanding general demand for substrates, there has also been a continuing reduction in size of electronic components and an increase in the number of circuits, and therefore electrical connection points required on each substrate. As such, the number of and density of solder connection points on substrates has substantially increased. As compared to substrates manufactured several years ago, today""s substrates used for IC chips or semiconductors has substantially more and higher density solder connection points. It is expected that such miniaturization of substrates and an increase in the required solder connection points will continue into the future.
As demands of higher speed and more sophisticated electronic devices has expanded, the respective demands for precise placement and reflow of solder material onto substrates used in manufacturing the devices has likewise grown. Attempting to keep pace with these demands, the technology of delivery and reflow of solder material has also been developing.
Representative prior art includes U.S. Pat. No. 5,467,913 issued to Namekawa et al. for a Solder Ball Supply Device. The Namekawa et al. device uses a discharger with a matrix of solder ball holding cavities, a head section having a number of air suction holes, and a solder ball supply means to take out, at one time, a large number of solder balls from the holding cavities and to place them, at one time, onto a substrate board. While this device may be able to place a number of solder connection points onto a substrate at one time, the device does not allow for easy alteration or modification of the patterns or matrices of solder connection points.
A different method of placing and bonding solder to a bonding surface is shown by the apparatus and process disclosed in U.S. Pat. No. 5,653,381 issued to Azdasht for a Process And Apparatus For Producing A Bonded Metal Coating. The Azdasht device uses specific solder material that may be transported within a capillary to a bonding surface by a physical stamp guided within the capillary. The physical stamp may also be an energy transfer device used to bond the solder material to the surface after it is xe2x80x9cstampedxe2x80x9d into place. While the xe2x80x9cone at a timexe2x80x9d placement and bonding of the solder appears to allow for easy reconfiguration of solder connection patterns between substrates, the device and method do not appear to be suitable for the high speed bonding required for mass production of substrates. Indeed, the Azdasht U.S. patent provides that an object of the device is for xe2x80x9cpilot or same-scale productionxe2x80x9d runs. PCT application WO 97/20654, for a Process And Device For Applying A Solder To A Substrate Or Chip Without Flux, also having as its inventor Ghassem Azdasht, is a German application. The Abstract, in English, describes a process and device to clean a region on a substrate and remelt solder to the substrate.
Devices similar to that described in the Azdasht U.S. patent are available from PAC TECH, Packaging Technologies GmbH. Such xe2x80x9csolder ball bumper bondheadxe2x80x9d machines are limited to ball placement and bonding rates of approximately 2 balls per second. As noted, with the reduction in the size of IC chips and semiconductors, and the circuits contained therein, and with the increase in the number of solder connections required to be on each substrate, there is a need for increased production speeds to place and bond or reflow solder balls to a substrate.
Accordingly, there remains a need for reliable and repeatable high speed delivery and reflow of solder connection points, or solder balls, onto substrates. Such reliability and repeatability is necessary for mass production of IC chips and semiconductors. Moreover, there is a need for such high speed delivery and reflow of solder balls with the flexibility of easy reconfiguration of the solder connection point patterns between different substrates.
In view of the shortcomings of the prior art, it is an object of the present invention to improve the speed, reliability and repeatability of delivering and reflowing solder material to a substrate. It is a further object of the present invention that the apparatus and method provide high speed capability of delivery and reflow of solder material necessary for mass production of substrates. Yet another object of the present invention is to permit easy and flexible modification of the solder material pattern on a substrate through use of a computer processor.
In a preferred embodiment, the present invention is an apparatus for delivering and reflowing solder material onto a substrate, comprising a stationary reservoir to hold the solder material; a capillary for guiding the solder material to the substrate; a flexible feed tube coupled to the reservoir for directing the solder material from the reservoir to the capillary; indexing means coupled to the feed tube and the capillary to individually index the solder material from the feed tube into the capillary; deliver means to deliver the solder material from the reservoir, through (a) the feed tube, (b) the indexing means, (c) the capillary and onto the substrate; and an energy source coupled to the capillary to reflow the solder material onto the substrate. In one preferred embodiment, the energy source is a laser.
According to another aspect of the invention, the delivery means comprises a pressurized fluid introduced into the reservoir to urge the solder material through the feed tube, through the indexing means, through the capillary and onto the substrate. The pressurized fluid, in preferred embodiments may be an inert gas, such as nitrogen.
According to still another aspect of the invention, the feed tube comprises a first tube and a second tube within the first tube, such that the second tube is substantially centered within the first tube, the second tube being for delivery of the solder material from the reservoir and the first tube for delivery of the pressurized fluid into the reservoir.
According to yet another aspect of the present invention, the reservoir incorporates sensing means to monitor the level of solder material in the reservoir.
According to a further aspect of the present invention, the indexing means individually indexes solder balls at a speed of about 200 solder balls per second.
According to yet another aspect of the present invention, the delivery and reflow of the solder balls is approximately 40 balls each second.
According to still another aspect of the present invention, the energy source includes a sensor to monitor the energy level delivered by the energy source.
According to another aspect of the present invention, a method of delivering and reflowing solder material onto a substrate, the method comprising the steps of: (a) urging solder material held in a stationary reservoir through a flexible feed tube by a pressurized fluid; (b) individually indexing the solder material from the feed tube into a capillary; (c) directing the individual solder material through the capillary to the substrate; and (d) reflowing the individual solder material to the substrate with an energy source.
These and other aspects of the present invention are set forth below with reference to the drawings and the detailed description of certain preferred embodiments.